It is known in the art to oxidize phenol to p-benzoquinone with oxygen in the presence of a copper ion catalyst and such a process is disclosed in U.S. Pat. No. 3,987,068. In that patent the oxidation is carried out in a nitrile solvent using a complex formed from the copper catalyst and the solvent and the operating conditions are said to be at temperatures of from about 0.degree. to 100.degree. C. and a partial pressure of oxygen of from about 7 to 200 (preferably 14 to 100) atmospheres. As pointed out in U.S. Pat. No. 3,987,068, yield of quinone product increases with increased partial pressure of oxygen and it appears from the data therein that partial pressures of oxygen above about 100 atmospheres are required in order to achieve conversions of phenol to p-benzoquinone on the order of about 75%. Such pressures are too high to be useful in an economical commercial process because they require special equipment of high capital cost.
U.S. Pat. No. 4,208,339 discloses a process for the preparation of p-benzoquinone by oxidation of phenol in the presence of cuprous or cupric ions and in the presence of a metal in the metallic form in a nitrile, amide, alcohol or sulfoxide solvent. Reaction rate is said to be increased by including an alkali metal or alkaline earth metal halide.